Some aircraft propeller blades are comprised of an airfoil surface and a spar/foam subassembly which is encased by the airfoil surface. The airfoil surface may comprise a fiber reinforced skin which is preformed as a shell or is formed by wrapping layers of a fiber matrix about the spar/foam subassembly. The spar/foam subassembly, which forms the main structural member of the blade, is comprised of a spar, formed typically of aluminum or the like, and a thermoset foam disposed at the leading and trailing edges of the spar. The spar extends along a substantial length of the airfoil surface and includes a root portion by which the blade is attached to a hub.
To manufacture a finished propeller blade, the subassembly is covered or wrapped with the fiber reinforced skin which is impregnated with a resin and cured. To manufacture the subassembly, a release agent is sprayed within a mold. A thermoset adhesive, which acts as a relatively finished surface for the subassembly, is sprayed upon the release agent. The mold is masked to avoid overspray of the adhesive thereby minimizing cleanup and maintaining tolerances within the mold. The spar is placed in the mold and the mold is heated to about 250.degree. F. for a given time to cure the adhesive. After the mold is cooled to about 150.degree. F., the thermoset foam is injected within the mold along the spar leading and trailing edges. The mold is then heated to about 250.degree. F. for a given time to cure the foam. Upon removal, the subassembly may be exposed to ultra-violet light to reveal any release agent disposed thereon. The spar/foam subassembly is then abraded to remove surface contamination and to texture the surface for subsequent bonding to the airfoil surface.
Several problems with the method exist: the cured adhesive may delaminate from the foam providing a poor subassembly surface thereby; the cured adhesive must be reworked to provide a bonding surface for the airfoil surface; the cured adhesive is opaque thereby concealing defects in the underlaying foam; the adhesive coating may break during handling causing rework; the amount of surface contamination of the subassembly is undesirable because of interaction between the release agent and the sprayed adhesive; the spar is heated for a prolonged period which is undesirable if further heat treating is required; and, excessive time and energy is required to heat and cool the mold to cure the adhesive.
Accordingly, a new method of manufacturing a spar/foam subassembly, and a new spar/foam subassembly is sought.